How many solar panels do you need for your RV? (And how do I charge the batteries?) Like so much else, it depends on many factors that are unique to every RVer: what type of rig, size, where, how, and when they use their RV. There are also many different types of solar panels to choose from.
I know, the shortest answer is not very helpful, but it comes down to how much you can afford, what you can fit in the space available, and where you want to put your solar panels. Solar panels are rated based on ideal conditions that rarely, if ever, occur in the real world.
You should generally expect to obtain much less than the full rated panel power. A solar panel’s rated power is at its peak in full sun when pointed exactly at the sun under ideal conditions—which almost never happens. In the real world, panels are not perfectly pointed at the sun or in cool weather with no clouds or moisture in the air to block some of the solar energy.
You should plan on 50-70% of the rated panel power, and less at other times of day, season, and different weather and geographic locations, accounting for real-world conditions. A 100W panel might be expected to produce an average of 50 or 60 watts for 5 hours per day, or 250 to 300Wh (watt-hours) per day in the summer. Roof-mounted panels might provide even less due to shading from an air conditioner, foliage, and other constraints.
Energy from an example system
For example, I have a 30-foot Class A motorhome with six 200-watt panels (1200W total) flat-mounted on the roof. They generally provide about 3000Wh per day in the summer when located in the Southwestern U.S.
When combined with 400W of portable panels they provide 1500Wh per day, if I keep moving them every few hours to point toward the sun. That’s a total of 4500Wh per day, which is a good match for our actual power usage, which is generally in the range of 3000-5000Wh per day.
Our 5-year-old RV also has a built-in generator, and we have generally used it less than 40 hours per year when traveling about 3-4 months per year. Most of that was used when running our air conditioners when it’s hot and we are off the grid. We prefer boondocking on public lands over staying in RV parks whenever possible.
Three common ways to add solar power to your RV
There are three common ways to add solar power to your RV: portable solar panels, often paired with a ready-to-use power station; permanently mounted panels on your roof; or a combination of both for maximum convenience, flexibility, and expansion.
A future additional option will become available by integrating solar power into an RV awning.
Solar panels are only part of a power system solution. Solar panels provide energy that must be controlled by a special battery charger to properly charge your house batteries. You may also want an inverter to allow conversion of DC battery power to 120Vac to run regular household appliances.
Portable solar panels and power stations
For a beginner, using portable folding solar panels with a portable power station or power bank (sometimes these are referred to as solar generators, but they only store and convert energy and do not actually generate it) is the easiest and least complex approach to start out with. And you can take the panels and power station with you to use elsewhere, or if you sell your RV.
If you measure your actual energy usage as described in my article series titled “Don’t pay for more solar than you need,” you can choose the right number of panels and the right size power station for your needs.
Even if you choose to mount solar panels on the roof later, you can keep the portable panels and put them out in the sun when your RV is parked in the shade. You can start small and add panels as your budget allows.
Portable power stations
These panels are also a good match to charge portable power stations. Power station energy capacity is rated in Wh (watt-hours) or kWh (thousands of Wh), indicating how much energy they store in their internal battery. They are also rated to provide peak 120Vac (Volts alternating current) power that they can deliver in watts. These units range from small, truly portable units providing a few hundred watts of power and a few hundred watt-hours of energy and weighing 5-10 pounds, to large, marginally luggable >50 lb. units providing thousands of watts and watt-hours.
A wide range of power stations are available that provide 12-volt DC and 120Vac power outlets with solar panel inputs for charging and various outputs such as a 12V lighter socket, USB power, and 120Vac outputs as shown in the example below.
It’s important to match the solar panels you use with a power station or the power bank could be damaged by solar panels that exceed the maximum input voltage of the power station.
Roof-mounted solar panels
Power stations are limited and cannot easily be upgraded. Installing a dedicated solar, battery, and power system is expandable, and usually more convenient and cost-effective than a power station of the same size.
If you plan to mount solar panels permanently on the roof of your RV, it makes sense to use a solar battery charger (MPPT or Maximum Power Point Tracking is best) to charge the house batteries and an inverter to provide 120Vac instead of a power station; they will become a permanent part of the rig. That setup is likely to stay with the RV when you sell it.
It’s usually best to plan the layout of roof-mounted panels to fit as many as possible, leaving space to add more panels if you don’t cover the roof completely to begin with. And that’s not far from what you’ll want if you like to boondock on public lands for days at a time.
Solar panels are relatively inexpensive compared to other components of an off-grid RV power system. Also, they typically only produce a fraction of their rated peak power, so more is usually better. Roof-mounted panels should be laid out in a way to allow someone to walk on the roof to do routine maintenance, access A/C units, etc.
One big advantage of roof mounting your solar panels is that they can charge your house batteries all the time, even when you’re in motion on the road or parked on the way to your next stop.
Optimize solar charging of your battery bank
For maximum charging speed, the solar panel output current should be near or slightly higher than the rated input current for a power station. The solar panel output voltage must be less than the maximum the station can accept.
The power station will limit the input charging current to be less than or equal to its rated capacity. Power stations also include internal battery charging circuits to accept solar power, 120Vac input, and 12Vdc vehicle power sources to charge the internal battery. They usually have a built-in inverter to convert their internal DC battery voltage to power 120Vac appliances.
The primary disadvantages of a portable power station are that you must generally replace it with a larger, more expensive unit if you want to upgrade, and you must deploy and store the portable panels and wires every time you set up or break camp. Because it’s relatively portable, you can take it with you, but high-power units with large batteries can be very heavy.
Solar awnings
Another relatively recent option to add solar to your rig is to install an awning that incorporates an integrated solar panel. It’s still pretty early days for these products, but it’s much easier to deploy and retract than portable panels, usually at the touch of a switch. A future article will cover solar awning product options in detail, but these are not quite ready for large-scale distribution at the time of writing.
In place of a power station option, next time we’ll cover the other elements of a dedicated solar power system aside from the solar panels: solar charge controllers and inverters.
RELATED
- Don’t pay for more solar than you need
- Don’t pay for more solar than you need, part two
- Don’t pay for more solar than you need, part three
- Solar controllers versus solar inverters
- Cheap, DIY solar generator setup
RVT1218
Absolutely zero solar panels. We never boondock, we only will go where there are 50 amp hookups! Stopped camping and bought a Class A and that is our choice nowadays!
Congratulations on getting your rig! As long as you can find places to stay when and where you need them, and don’t need to be off the grid when you are in between, then $0 is an unbeatable cost.
In our area, finding such places requires planning and booking way in advance, which is now much more difficult than it was before Covid.
Thank you for the series of articles, Ken! They are well-organized and broken into pieces of the story that are fairly easily digested. Have a great week and safe travels!